This invention relates to optical fibres and in particular, but not exclusively, to optical fibres for sensor applications.
Optical fibres can become lossy when subject to deformations. In multimode fibres so-called microbending sensors can be constructed by applying a periodic (spatial) deformation (with a magnitude linked to the magnitude of the quantity being sensed) to the fibre. The optical loss is dependent on the period of deformation and has a sharp maximum. In monomode fibre a similar effect occurs, and in this case the deformation period for maximum loss depends on wavelength. The deformation of the optical fibre is generally obtained as a result of its being pressed, by the perturbation to be sensed, onto a machined grating or machined mandrel. Such sensor systems are disclosed in our U.K. Application No. 8222371 (Serial No. 2125572) (R. E. Epworth-V. A. Handerek 24-1) and No. 8405853 (Ser. No. 706,309) (R. E. Epworth-R. J. Brambley 26-1).